Electron beam production system for electronic discharge vessels



July 1. 1969 H. KATZ 3,453,430

ELECTRON BEAM PRODUCTION SYSTEM FOR LLBCTRONIC DISCHARGE VESSBLS Filed March 22, 1967 Fig. 2 I 1 Fig.3

[ZZZ/IZZZOZ figZzzzzzZ M548 United States Patent 3,453,480 ELECTRON BEAM PRODUCTION SYSTEM FOR ELECTRONIC DISCHARGE VESSELS Helmut Katz, Munich, Germany, assignor to Siemens Aktiengesellschaft, a corporation of Germany Filed Mar. 22, 1967, Ser. No. 629,859 Claims priority, application Germany, Mar. 26, 1966, S 102,856 Int. Cl. HOlj 1/20, 19/14 US. Cl. 313-337 13 Claims ABSTRACT OF THE DISCLOSURE The invention relates to an electron beam production system for electron discharge vessels, in particular HF power tubes, in which system the beam cathode, in the form of a cathode with frontal porous carrier disk for the emission substance receives its heating energy, through cathodic bombardment, from an auxiliary cathode arranged therebehind.

It is of particular importance for HF high power tubes operating with an electron beam. For this type tube, for example, for traveling wave tubes of high power, among others, a primary difliculty resides in maintaining the electrodes required for the beam formation, which are directly adjacent to the cathode, sufliciently cool that they do not radiate any thermal emission even when vaporizing emission promoting substances. In such a production system it is therefore required that the quantity of heat passing from the cathode to the most closely adjacent electrodes, in particular to the control electron, be as small as possible. For this purpose, among other things, not only the volume and surface of the cathode, but also the filament power to be transmitted to it, should be as small as possible.

This is sought to be achieved in a specific manner with respect to a previous electrode system arrangement in which the heating of the beam cathode is elfected by cathodic bombardment from an auxiliary cathode which supplies the active substance for the principal (beam) cathode, in which case a much smaller auxiliary cathode is sufficient for the activation of the beam cathode. For this reason in particular, this type of cathode has been utilized, it being especially noted, however, that nothing funda mental changes-if the principal cathode also has a supply of its own. Through such an arrangement of two cathodes arranged one behind the other, not only the customary difliculties, connected with the usual, continuously operated heater of the principal cathode, such as insulation disturbances, heat dissipation,.etc., are divided but in ad dition to this further advantages are rendered possible. That is to say, while the heater for the auxiliary cathode is completely separated from the principal cathode itself and therefore cannot cause any immediate difiiculties for such principal cathode, a heater element always constitutes a possible weak spot in the entire structure of the electronic discharge vessel, in particular with respect to its useful operating life, in the electron beam production system.

It is, therefore, the object of the invention to attain, through constructive design and special selection of ma- 3,453,480 Patented July 1, 1969 terial, an electron beam production system which is, at least in its normal operating state, able to operate without heating means which must be continuously operated from a special energy source.

In an electron beam production system for electron discharge vessels, in particular for HF power tubes, such as initially described, in which system the beam cathode receives its heating energy from an auxiliary cathode through cathodic bombardment this is accomplished, according to the invention, attained by the feature that the cathode carrier, in the form of a cathode body cooperable with both cathodes is constructed to provide such good heat conduction that in the normal operating condition the additional heat derived solely from the heating effected through the electron discharge gap is sufficient for the heating of the auxiliary cathode and that there is additionally provided special warm-up means, preferably automatically disconnectible.

The invention is based upon the following background:

The walls of the cathode body of the principal cathode, forming a mounting cover or enclosure, consist of a material which is sufficiently heat conducting, such as for example, molybdenum or carbon with an enlarged wall structure, whereby the temperature assumed by the porous disk during operation through the cathodic bombardment is transmitted to such walls. If it is additionally efiected that a portion of the electron discharge flow proceeding from the auxiliary cathode is received at such walls, the emission substance carrier disk as well as the walls of the cathode attain approximately the same temperature in spite of heat radiation. Since the auxiliary cathode is substantially enclosed in the cathode carrier of the beam cathode serving as a mounting cover, such auxiliary cathode likewise assumes approximately the same temperature as the principal cathode. Consequently when the principal cathode has assumed its normal operating temperature through cathodic bombardment, the auxiliary cathode also assures this same temperature and does not require additional heat. Of course, this presupposes the use of two approximately similar cathodes in which case the operating temperature of the auxiliary cathode should be approximately the same or somewhat lower than that of the principal cathode. An electron beam production system operating in such a manner without an individual heater in its normal operation becomes especially advantageous or may be practical only through the use of two metal capillary cathodes, since for example, a normal oxide cathode would be much too sensitive as an auxiliary cathode and would not be matched to the high current requirements for the delivery of the cathodic bombardment. In addition, a greater difference in the operating temperature of both cathodes would require means diificult to fulfill to correctly control the respective operating temperatures relative to one another and would be completely impossible if the auxiliary cathode would have to be hotter. Consequently, such an electron beam production system in normal operation represents an arrangement with considerable additional advantages. For example, for each of the two cathodes only a single conductor lead is required between which an appropriate voltage is applied without necessitating a continuous heater.

Details of the means according to the invention by which the operational state of such an electron beam production system is obtained are explained by means of the examplesof construction, purely schematically illustrated in the drawings. Parts which do not obsolutely contribute to the understanding of the invention have been omitted or are not designated in these drawings.

Referring to the drawings, in which like reference characters designate like or corresponding parts:

FIG. 1 is a longitudinal or axial section through a cathode system embodying the invention and utilizing a starting heater;

FIG. 2 is a section similar to FIG. 1 of an embodiment utilizing induction heating for the starting means; and

FIG. 3 is a section similar to FIGS. 1 and 2 of a further embodiment of the invention.

FIG. 1 illustrates an example of construction according to the invention in which the auxiliary heater is directly associated with the principal (beam) cathode, and has the special advantage that considerably more space is available for the disposition of the heater itself and in addition thereto the distance between the mounting cover or cathode body and the inner auxiliary cathode, determinative for heat economy, can be made sufficiently small. The porous carrier disk for the emission substance designated by the reference numeral 1 represents basically the actual electron beam cathode, i.e., the principal cathode. It has a relatively large emission surface and is inserted at the end of a portion 3, enlarged to form a truncated cone, of a hollow cathode carrier 2 of generally cylindrical construction and made, for example, of molydenum, defines a frontal plane at said disk. Disposed within the cathode carrier 2 is a cathode 11, preferably cylindrical, which likewise is provided with a frontal porous emission substance carrier disk 12 arranged coaxially as auxiliary cathode with such disk being disposed in the extended cylindrical part 4 of the cathode body 2. Such auxiliary cathode has a customary sufficiently large longitudinally extending supply space in which is contained the supply emitting the active substance. It has, however, no directly associated heater or even a heater attached thereto. Instead a heater spiral 5 principally wound around the exterior of the cylindrical part 4 of the cathode carrier is provided on the cathode carrier 2 of the principal cathode approximately in the locality corresponding to the longitudinal extent of the auxiliary cathode which heater spiral is cemented or imbeded in with an insulating substance 7, within a shield cover 8 for protection from radiation, and consists of a tungsten wire provided with an insulating coating 6. To achieve an especially good heat transmission, the immediate insulating coating of the heating wire as well as the insulating body efiecting the imbedding can with particular advantage consist principally of beryllium oxide instead of the otherwise customary aluminum oxide.

After the heating up of the electron beam system with the auxiliary heater 5, an electron discharge takes place between the two porous emission substance carrier disks 1 and 12, during which not only the emission substance carrier disk 1, but also the cathode body 2 are heated through the cathodic bombardment, and as a result the good heat conduction of the cathode body 2, the auxiliary cathode 11 is likewise sufiiciently heated, even if the heating up device is disconnected in such operational state, preferably automatically through special means therefor. The auxiliary heater can be electrically dimensioned in such a manner that it can be connected in parallel with the electron discharge gap operating for the cathodic bombardment. For the avoiding of unnecessary heat losses, the feed line 13 for the auxiliary cathode can be provided with shield plates 14. The feed line 9 for the principal cathode can be effected in customary manner over the cover 8, for protection from radiation, together with one lead for the auxiliary heater. The illustrated arrangement of the heater disposed on the cathode body of the principal cathode has several advantages, especially if an on-off or regulation device is provided. More particularly, as the heater acts upon the principal cathode, the temperature of this cathode determinative for the system can be directly or indirectly employed as a reference magnitude for the regulation process. That is to say after the cathode jacket 2 with its parts 3 and 4 has assumed the final temperature specified therefor,

the temperature of the heater has also increased from its initial temperature at the beginning of the warm-up process in such a manner that it tends to approach a maximum value. Such a specified, available maximum value of the operating temperature can be utilized as a control magnitude for the on-off control of the operating voltage at the heater.

FIG. 2 illustrates another example of construction, in which instead of a heater spiral, a coil 5 is provided to which a high frequency cement is conducted for the inductive warm up heating of the cathode body 2 of the auxiliary cathode 11. Since such coil has no direct contact with the cathode body, it consequently does not represent a heat dissipation for the cathode, and the coil itself can be of rather heavy construction. In this case the lower cylindrical part 4 of the cathode jacket 1 may be inductively heated and then the auxiliary cathode 11 may be heated, so to speak, indirectly therefrom, or the auxiliary cathode may be heated directly in inductive manner by providing the predominantly cylindrical part 4 with several narrow slots 10 at the location of the coil. A thermocouple element mounted on the shell for protection from radiation can be utilized for switching the inductive heating element on or off.

The invention is not limited to the example of construction illustrated in FIGS. 1 and 2, but can be additionally considerably varied. For example, as illustrated in FIG. 3, the principal cathode as well as the auxiliary cathode or even both cathodes can at their lower parts be provided with a porous carrier disk 1' and 12 for emission substance, in which case, as indicated in the drawing, the auxiliary cathode can also :be completely enclosed by the principal cathode in tight manner, although not necessarily. The embodiment illustrated in FIG. 3 has the following special characteristics. In this embodiment the auxiliary cathode supplies double the quantity of barium for the two porous emission substance carrier disks 1, 1' of the principal cathode. This can be especially advantageous or even required if for example the surfaces of the emission substance carrier disks of the principal cathode exceed a dimension which can be still supplied sufficiently with barium from a single disk of an auxiliary cathode. In this case the lower emission disk of the principal cathode can be utilized for a function other than for beam production, for example, for cathodic bombardment of a molybdenum or carbon disk, covered with zirconium. The second emission substance carrier disk 12' of the auxiliary cathode in addition to this also makes it possible to simultaneously heat the principal cathode through cathode bombardment from both sides, i.e., from the top and from the bottom.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected 'by Letters Patent.

I claim:

1. An electron beam production system for electron discharge vessels, comprising a principal cathode in the form of a porous emissive disk, an auxiliary cathode in the form of a second porous emissive disk spaced from the principal cathode forming an electron discharge gap therebetween, cathode carrier means for supporting the principal cathode at one end thereof and enclosing the auxiliary cathode within the cathode carrier and positioned to bombard the principal cathode with electrons, said cathode carrier means conducting the heat generated within the discharge gap between the two cathodes and transmitting the heat to the auxiliary cathode in order to maintain the auxiliary cathode at an operating temperature, and heating means for bringing the auxiliary cathode up to operating temperature.

2. An electron beam production system according to claim 1, wherein said heating means comprises an auxiliary heater.

3. An electron beam production system according to claim 2, wherein the auxiliary heater, in the form of a heater spiral, is operatively disposed on the exterior of the cathode body adjacent the location of the auxiliary cathode disposed therewithin.

4. An electron beam production system according to claim 3, wherein the auxiliary heater is imbedded in an insulating material of high thermal conductivity, comprising beryllium oxide.

5. An electron 'beam production system according to claim 2, wherein the auxiliary heater is connected in parallel to the electron discharge gap effecting the cathodic bombardment, and correspondingly electrically dimensioned therefor.

6. An electron beam production system according to claim 2, wherein a control device forming a part of the heating means is coopera-ble with said auxiliary heater, for connecting and disconnecting the same.

7. An electron beam production system according to claim 1, wherein said heating means comprises an HP induction coil encircling a constructed part of the cathode body adjacent the location of the auxiliary cathode disposed therein.

8. An electron beam production system according to claim 7, wherein the constructed part of the cathode body is generally cylindrical and is provided with a plurality of narrow slots adjacent the location of the auxiliary cathode and the induction coil.

9. An electron beam production system according to claim 1, wherein the principal cathode structure forms a closed container with its cathode body functioning as a mounting structure, the second frontal end surface of such container also being constructed in the form of a porous carrier disk for emission substance, the supply container of the auxiliary cathode having a porous emission sub stance carrier disk terminating each respective end thereof.

10. An electron beam production system according to claim 1, wherein the beam cathode comprises a cathode :body and a porous carrier disk for emission substance which is supplied with emission promoting substance solely from that contained in the auxiliary cathode.

11. An electron beam production system according to claim 1, wherein the porous emission substance carrier disk of the beam cathode is in the form of a carbon body.

12. An electron beam production system according to claim 11, wherein all porous disks of the cathode structure are in the form of respective carbon bodies.

13. An electron beam production system according to claim 1, wherein said heating means further comprises means for automatically rendering such heating means inoperable when the temperature of said auxiliary cathode reaches its normal operating temperature.

References Cited FOREIGN PATENTS 643,655 9/1950 Great Britain.

JOHN W. HUCKERT, Primary Examiner. R. F. POLISSACK, Assistant Examiner.

U.S. Cl. X.R. 313338, 339, 340, 346, 356 

